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Grassy Silica Nanoribbons and Strong Blue Luminescence

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ABSTRACT

Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

No MeSH data available.


Formation of silica nanoribbons and various fine structures.(a) SEM image showing initial formation of silica nanoribbons at the melted crack-wall sites. (b) SEM image showing a bunch of silica nanoribbons together with nanowires. (c) SEM image showing nanoribbons with different morphologies and deformation of nanoribbons by electron-beam. (d) SHIM image highlighting different edge structures of nanoribbons. (e) SHIM images showing dense nanoribbons. (d) tilt-view of bunched silica nanoribbons.
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f3: Formation of silica nanoribbons and various fine structures.(a) SEM image showing initial formation of silica nanoribbons at the melted crack-wall sites. (b) SEM image showing a bunch of silica nanoribbons together with nanowires. (c) SEM image showing nanoribbons with different morphologies and deformation of nanoribbons by electron-beam. (d) SHIM image highlighting different edge structures of nanoribbons. (e) SHIM images showing dense nanoribbons. (d) tilt-view of bunched silica nanoribbons.

Mentions: We found the formation of silica nanoribbons when heating very thin Cr films deposited on SiO2/Si substrates under S atmosphere. However, without either Cr or S, no silica nanoribbon could be obtained. It is a big surprise, to some degree, because a thin Cr layer is normally an adhesive layer of the source/drain electrodes for field-effect transistors on SiO2/Si platform24. In the literature, the production of monolayer or bilayer 2D silica depended only on the metals and no S was present in their reaction systems1112131425262728. Therefore, we believed that Cr and S acted as the dual co-catalysts for the growth of silica nanoribbons. Furthermore, on the basis of the morphological observation of the different phases of the growth, the growth mechanism of silica nanoribbons is most likely to be as follows (see Fig. 3 and Figure S6 in Suppl. Info.). Cracks were firstly generated in the SiO2 layer on Si with the assistance of Cr and S at high temperature (Fig. 3a); melting of the SiO2 occurred at the wall of the SiO2 cracks; and nanoribbons grew in-situ at the crack sites. It is also sound from the observations that the Si and O sources for the formation of silica nanoribbons were originated from the melted SiO2. The formed silica nanoribbons exhibit various features. Some nanoribbons like a braid (Fig. 3b,c), and some have wedge-shaped edges (Fig. 3d). It is also observed that long silica nanowires with size of about 20 nm (Figure S6e, Supp. Info.) were produced together with the nanoribbons (see Figs 2c–e and 3). In addition, short silica rods were also produced, lying on the substrate (see Figs 2c–eand 3). The generation of these silica nanostructures on the SiO2 substrate is rather interesting and the grassy appearance of the silica nanostructures is quite astonishing. The silica nanoribbons are bendable. Moreover, the nanoribbons are sensitive to the exposure of electron beam. As demonstrated in the sequentially acquired AES mappings in Fig. 2c–e, the nanoribbons highlighted in the oval were movable under the electron beam irradiation, which indicates the possibility to manipulate the nanoribbons by electron beam. Also, excessive exposure of electron beam could damage the nanoribbons as observed in Fig. 3b,c. Our grassy silica nanoribbons show distinct morphological characteristics from previous reported silica nanostructures such as nanowires29 and twisted nanobelts and nanosprings30 synthesized by a thermal evaporation method at 1300 °C, porous nanostructures synthesized by complicated solution chemical reactions31, and silica nanotubes synthesized by a template-directed method32.


Grassy Silica Nanoribbons and Strong Blue Luminescence
Formation of silica nanoribbons and various fine structures.(a) SEM image showing initial formation of silica nanoribbons at the melted crack-wall sites. (b) SEM image showing a bunch of silica nanoribbons together with nanowires. (c) SEM image showing nanoribbons with different morphologies and deformation of nanoribbons by electron-beam. (d) SHIM image highlighting different edge structures of nanoribbons. (e) SHIM images showing dense nanoribbons. (d) tilt-view of bunched silica nanoribbons.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f3: Formation of silica nanoribbons and various fine structures.(a) SEM image showing initial formation of silica nanoribbons at the melted crack-wall sites. (b) SEM image showing a bunch of silica nanoribbons together with nanowires. (c) SEM image showing nanoribbons with different morphologies and deformation of nanoribbons by electron-beam. (d) SHIM image highlighting different edge structures of nanoribbons. (e) SHIM images showing dense nanoribbons. (d) tilt-view of bunched silica nanoribbons.
Mentions: We found the formation of silica nanoribbons when heating very thin Cr films deposited on SiO2/Si substrates under S atmosphere. However, without either Cr or S, no silica nanoribbon could be obtained. It is a big surprise, to some degree, because a thin Cr layer is normally an adhesive layer of the source/drain electrodes for field-effect transistors on SiO2/Si platform24. In the literature, the production of monolayer or bilayer 2D silica depended only on the metals and no S was present in their reaction systems1112131425262728. Therefore, we believed that Cr and S acted as the dual co-catalysts for the growth of silica nanoribbons. Furthermore, on the basis of the morphological observation of the different phases of the growth, the growth mechanism of silica nanoribbons is most likely to be as follows (see Fig. 3 and Figure S6 in Suppl. Info.). Cracks were firstly generated in the SiO2 layer on Si with the assistance of Cr and S at high temperature (Fig. 3a); melting of the SiO2 occurred at the wall of the SiO2 cracks; and nanoribbons grew in-situ at the crack sites. It is also sound from the observations that the Si and O sources for the formation of silica nanoribbons were originated from the melted SiO2. The formed silica nanoribbons exhibit various features. Some nanoribbons like a braid (Fig. 3b,c), and some have wedge-shaped edges (Fig. 3d). It is also observed that long silica nanowires with size of about 20 nm (Figure S6e, Supp. Info.) were produced together with the nanoribbons (see Figs 2c–e and 3). In addition, short silica rods were also produced, lying on the substrate (see Figs 2c–eand 3). The generation of these silica nanostructures on the SiO2 substrate is rather interesting and the grassy appearance of the silica nanostructures is quite astonishing. The silica nanoribbons are bendable. Moreover, the nanoribbons are sensitive to the exposure of electron beam. As demonstrated in the sequentially acquired AES mappings in Fig. 2c–e, the nanoribbons highlighted in the oval were movable under the electron beam irradiation, which indicates the possibility to manipulate the nanoribbons by electron beam. Also, excessive exposure of electron beam could damage the nanoribbons as observed in Fig. 3b,c. Our grassy silica nanoribbons show distinct morphological characteristics from previous reported silica nanostructures such as nanowires29 and twisted nanobelts and nanosprings30 synthesized by a thermal evaporation method at 1300 °C, porous nanostructures synthesized by complicated solution chemical reactions31, and silica nanotubes synthesized by a template-directed method32.

View Article: PubMed Central - PubMed

ABSTRACT

Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

No MeSH data available.